Carbolithiation of styrenes with N-tert-butyl aldimines

Article abstract of DOI:10.3184/174751912X13528268645571

The addition of aldimine anions to styrene occurs upon the treatment of N-tert-butyl aldimine with LDA followed by the addition of styrene to give the corresponding aldehyde after hydrolysis. Cyclohexenyl amines are generated when the reactions are performed with unsaturated aldimines. This approach affords 4-phenyl substituted butanals and cyclohexenyl amines in a simple and inexpensive way.

Full text of DOI:10.3184/174751912X13528268645571

732 RESEARCH PAPER
DECEMBER, 732–735
JOURNAL OF CHEMICAL RESEARCH 2012
Carbolithiation of styrenes with N-tert-butyl aldimines
Jie Liu and Hai-Shan Dang*
Fragrance Science &Technology, Givaudan Fragrances (Shanghai) Ltd, 298 Li Shi Zhen Road, Shanghai 201203, P. R. China
The addition of aldimine anions to styrene occurs upon the treatment of N-tert-butyl aldimine with LDA followed by
the addition of styrene to give the corresponding aldehyde after hydrolysis. Cyclohexenyl amines are generated
when the reactions are performed with unsaturated aldimines. This approach affords 4-phenyl substituted butanals
and cyclohexenyl amines in a simple and inexpensive way.
Keywords: C2-Elongation, carbolithiation, aldimine anion, styrene, cycloalkenylation
C2-Elongation by the chemistry of α-deprotonated aldimines
finds broad applications in organic chemistry.1 The aldimines
deprotonated with a base (Stork’s approach2) or specifically
with LDA (Wittig’s approach3) react with an electrophile,
usually an alkyl halide in most cases, to give the α-alkylated
products.
In view of reagent and environmental costs, the use of a
simple alkene instead of an alkyl halide is desirable. In the
exploration of the area, Nakamura and coworkers reported4
an enantioselective synthesis of α-alkylated cyclohexanones
through three-component coupling of an optically active zinc
enamide with alk-1-enes and an electrophile. The key step
involves the addition of a zinc enamide to an unreactive alkene.
Matsubara and Kobayashi reported5 that Cu(OTf)2-catalysed
stereoselective carbon–carbon and carbon–nitrogen formation
by reaction of N-acylimino esters, glyoxylates, aldehyde-
ketone derivatives and iminophosphates with enamides and
enecarbamates which act as nucleophiles. The reaction
proceeds by a non-concerted aza-ene type pathway which is
facilitated by Cu-coodination between N-, O- or P-atoms on
the substrates.
In the meantime, carbolithiation enjoys widespread use in
the chemistry of carbon–carbon bond formation.6–9 This reac-
tion involves the addition of alkyl, vinyl and aryllithiums to
unactivated alkenes and alkynes, and can be viewed as a subset
of the broader family of carbometallation reactions.10,11
In spite of the wide range of applications of carbolithiation
in organic synthesis, the addition of lithiated aldimine anions
to alkenes has received relatively little attention. Marazano and
coworkers reported12 that deprotonated N-tert-butyl aldimines
react with vinamidinium chloride to give 2-alkylaminopenta-
dienimine derivatives, which are efficient intermediates for the
preparation of 3-substituted pyridines and the corresponding
hydrochloride salts. Other examples are the addition of the
lithiated N-isobutylidene-tert-butylamine to 1,3-dienes (buta-
diene, isoprene and myrcene) or an unsaturated aldehyde in
relatively low yield and limited substrate scope.13,14 We now
report a convenient approach to the preparation of 4-phenyl
substituted butanals and cyclohexenylamines via the addition
of tert-butyl aldimine anions to styrene.
obtained from the addition of different lithiated aldimines to
styrenes are tabulated in Table 1.
Double-addition compound 12 was produced when the
shorter chain aldimine 5 was subjected to the carbolithiation
conditions (entry 1 in Table 1). Mono-addition product 13 was
obtained when the sterically more hindered aldimine 6 was
used (entry 2 in Table 1). The reaction of ketimine 7 with
styrene (entry 3 in Table 1) gave product 14 as a consequence
of α-alkylation of the lithium ketimine. The reaction of α-
methylstyrene 9 with the aldimine anion was sluggish and
could only be slightly improved when the reaction was carried
out in the presence of 1 equiv. of TMEDA (entry 4 in Table 1).
Product 15 was isolated in 30% yield after hydrolysis of the
reaction mixture, but the reaction of 2-methylstyrene 10 with 8
afforded a good yield of 16 as shown in entry 5 in Table 1.
The vinylimidazole 11 was then selected as a heterocyclic
equivalent of styrene and subjected to the carbolithiation with
the aldimine 1. In this case product 17 was obtained in high
yield. Apparently the reaction proceeds via the addition of the
vinylimidazole anion to the aldimine in a manner described in
the LDA-mediated reaction of methylimidazole with propion-
aldehyde.15 The pKa of methylimidazole,16 being approxi-
mately 10 times larger than that of aldimines and ketimines,17
can be used to explain this preferred addition mode.
A possible mechanism for the reaction of LDA-promoted
styrene and aldimines is shown in Scheme 2.
Lithium-assisted ene processes are well known to occur in
organic reactions.18,19 The addition of styrene to the aldimine
anion is facilitated via the chelated species A. The ene reaction
gives the lithiated intermediate B, and eventually affords the
product after acidic hydrolysis. In the case of R=H (aldimine
5, entry 1, Table 1), a Li–H exchange between the intermediate
B and diisopropylamine occurs. The resulting aldimine, an
equivalent of the aldimine 1, reacts with styrene to give the
double addition product 12.
Subsequently, the unsaturated aldimines 18, 19 and 20 were
reacted with styrene. The results are shown in Table 2.
The cyclised products cis-21 and trans-22 were obtained
in a ratio of 1.2:1 when the α,β-unsaturated aldimine 18 was
used. The stereochemistries of 21 and 22 were determined by
1
comparison of the H NMR coupling constants between H-1
Results and discussion
In our exploration of efficient C–C-bond forming reactions in
the field of fragrance chemistry, we found that the lithiated
aldimine 1 reacted with styrene to give addition product 3
which was in turn transformed to 4 after hydrolysis as shown
in Scheme 1.
Albeit the newly formed aldimine 3 can be isolated in pure
form, further transformation to aldehyde 4 could be achieved
in a one-pot reaction upon treatment of the quenched aqueous
solution with oxalic acid and gave the 4-phenyl substituted
butanal 4 in a simple and inexpensive way. The products
Scheme 1 The addition of lithium tert-butylpropylaldimine to
* Correspondent. E-mail: hai-shan.dang@givaudan.com
styrene and subsequent hydrolysis.

JOURNAL OF CHEMICAL RESEARCH 2012 733
Table 1 Products from carbolithiation of styrenes with simple
aldimines
Table 2 Products from carbolithiation of styrene with unsatur-
ated aldimines
Entry
1
Aldimine
Styrene
Product
Yield
65%
Entry
Aldimine
Product
Yield
47%
2
1
2
3
2
2
40%
35%
2
3
45%
36%
4
5
1
30%
70%
6
1
95%
Conclusion
In conclusion, a simple and straightforward way to prepare 4-
phenyl substituted butanals has been established via carboli-
thiation of a styrene with an LDA-mediated aldimine. It can
be envisaged as a procedure for C2-elongation. Based on
this approach, derivatives of 4-phenylbutanal and 3-amine-
substituted 4-phenylcyclohex-1-ene can be readily prepared
from the approach with saturated and unsaturated aldimine
anions.
and H-2. These are 4.8 Hz at 3.04 ppm for 21 and 7.8 Hz at
3.20 ppm for 22. The larger coupling constant for 22 results
from the trans-coupling between H-1 and H-6 in the pseudo
chair configuration.20,21 The reaction of unsaturated aldimine
19 with styrene afforded cyclic amine 23 as a mixture of
isomers in a ratio of 6.2:1. NMR analysis confirmed the trans-
isomer to be the major product. Three addition products 24, 25
and 26 in a ratio of 1.2:1:1 were obtained when the reaction
was carried out with unsaturated aldimine 20. Compound 24
was isolated and identified by H–H COSY and C–H COSY.
The 13C NMR δ of 24 at 194.2 ppm indicates that there is
conjugation between the aldehydic carbon and the ring double
bond in contrast to the non-conjugated counterparts 25 and
26 in which the corresponding chemical shifts are 205.6 and
204.5 ppm respectively. The 13C NMR showed the chemical
shifts of C-2 for 25 and 26 to be 51.0 and 48.2 respectively.
Hence these two isomers 25 and 26 were assigned as shown in
Table 2 based on NMR analysis.
Experimental
1
IR spectra were recorded with a Bruker Tensor 27 instrument. H
NMR and 13C NMR spectra were recorded with Bruker AW 300 or
DPX 400 instruments in CDCl3. Chemical shifts are reported in δ
(ppm) relative to Me4Si (TMS). GC-MS spectroscopic data were
obtained from Agilent 6890 N and MSD 5975 instruments using
a HP-5 MS column. HRMS were obtained with a Bruker Microtoff
11 machine using an ESI source. Column chromatography was
performed on silica gel (200–300 mesh) from the Qingdao Ocean
Chemical Factory. All solvents and commercially available chemicals
were used as received.
The regioselectivity and the stereochemistry of cyclic prod-
ucts in the Table 2 can be explained by the mechanism as
shown in Scheme 3.
Apparently the internal double bond migration occurred in
the lithiation stage and consequently, the addition of styrene
to the anions at different positions afforded 24, 25 and 26 as
shown in Scheme 4.
N-tert-butylaldimines 1,22 5,23 6,24 7,25 8,26 18,27 1928 and 2026 were
prepared from the corresponding aldehyde and tert-butylamine
according to literature methods.
Reactions of aldimines and styrenes; general procedure:
The LDA solution was prepared separately by the addition of BuLi
(1.6 M, 19.0 mL, 30.0 mmol) to a solution of diisopropylamine (2.8 g,
Scheme 2 A possible mechanism for LDA-promoted reaction of styrene and aldimines.

734 JOURNAL OF CHEMICAL RESEARCH 2012
(C-2), 33.8 (C-4), 28.3 (CH), 27.7 (C-3), 20.1 (Me), 19.6 (Me); MS
m/z (%) 190 (M+, 2), 129 (2), 115 (2), 104 (100), 91 (48), 71 (22).
2-Phenethylcyclohexanone (14):34 Oil, IR (film, ν, cm−1) 1721
(C=O). 1H NMR (CDCl3, 300 MHz): δ 7.18–7.32 (m, 5H, Ph), 2.62 (t,
J = 7.8 Hz, 2H, CH2), 1.95–2.45 (m, 6H, 3 × CH2), 1.31–1.90 (m, 5H,
CH and 2 × CH2); 13C NMR (CDCl3, 75 MHz): δ 213.1 (C=O), 142.2,
128.4, 128.3, 125.8, 49.9 (CH), 42.1, 34.1, 33.2, 31.2, 28.1, 24.9; MS
m/z (%) 202 (M+, 5), 115 (2), 104 (6), 98 (100), 83 (16), 70 (17).
2-Methyl-4-phenylpentanal (15 as two diastereoisomers): Oil, IR
(film, ν, cm−1) 1722 (C=O), 1494, 1453. 1H NMR (CDCl3, 300 MHz):
δ 9.57 and 9.48 (two s, 1 H, CHO), 7.14–7.33 (m, 5H, Ph), 2.72–2.83
(m, 1H, H-4), 1.93–2.32 (m, 2H, HA-3 and H-2), 1.44–1.66 (m, 1H,
HB-3), 1.28 and 1.26 (two d, J = 7.7 Hz, 3H, 4-Me), 1.07 and 1.05
(two d, J = 6.8 Hz, 3H, 2-Me); 13C NMR (CDCl3, 75 MHz): δ 204.9(1)
and 204.8(5), 146.4 and 145.9, 128.6(2) and 128.5(7), 127.0, 126.4
and 126.3 (Ar C), 44.5 and 44.4 (C-2), 39.4 and 38.6 (C-3), 37.5 and
37.3 (C-4), 23.0 and 22.4 (4-Me), 14.1 and 13.2 (2-Me); MS m/z (%)
176 (M+, 2), 143 (1), 128 (1), 118 (100), 105 (65), 91 (20); HRMS:
Calcd for C12H16O[M + H+] 177.1274, Found: 177.1279.
Scheme 3 A possible mechanism for the formation of the
cyclic amines.
27.9 mmol) in THF (20 mL) with stirring at –78 oC under argon. The
resulting solution was warmed to RT and stirred for 20 min. It was
then added dropwise to a solution of 1 (3.0 g, 26.5 mmol) and styrene
(2.5 g, 24.0 mmol) in THF (30 mL) with stirring at −78 °C under
argon. The reaction mixture was warmed gradually to RT and stirred
for 8 h. The reaction was quenched with water (50 mL) at 0 °C. The
organic phase was separated and the aqueous phase was extracted
with ethyl acetate (3 × 20 mL). The combined organic phases were
washed with saturated sodium bicarbonate (20 mL), dried over
MgSO4. The solvent was removed by rotary evaporation, and the
remaining oil was distilled under reduced pressure to give 2-methyl-
N-(2-methyl-4-phenylbutylidene)propan-2-amine 3 as a light yellow
oil, b.p., 140 °C/1.5−1 mbar; IR (film, ν, cm−1) 1671 (C=N), 1453,
1364. 1H NMR (CDCl3, 300 MHz): δ 7.38 (d, J = 6.6 Hz, 1H, H-1),
7.14–7.30 (m, 5H, Ph), 2.51–2.64 (m, 2H, H-4), 2.31–2.42 (m,
1H, H-2), 1.60–1.85 (m, 2H, H-3), 1.17 (s, 9H, 3 × Me), 1.08 (d, J =
6.8 Hz, 3H, 2-Me). 13C NMR (CDCl3, 75 MHz): δ 163.0 (C-1), 142.4,
128.4, 128.3 and 125.7 (Ar C), 56.4 (tert-C), 39.7 (C-2), 36.3 (C-4),
33.5 (C-3), 29.7 (3 × Me), 17.8 (2-Me); MS m/z (%) 217 (M+, 1), 202
(4), 175 (1), 160 (2), 145 (11), 126 (8), 113 (100), 98 (78); HRMS:
calcd for C15H23N[M + H+] 218.1903; found: 218.1903.
2,2-Dimethyl-4-(o-tolyl)butanal (16): IR (film, ν, cm−1) 1720
1
(C=O), 1460. H NMR (CDCl3, 300 MHz): δ 9.52 (s, 1H, CHO),
7.09–7.14 (m, 4H, Ph), 2.46–2.57 (m, 2H, CH2), 2.29 (s, 3H, CH3),
1.68–1.77 (m, 2H, CH2), 1.15 (s, 6H, 2 × Me). 13C NMR (CDCl3, 75
MHz): δ 205.9, 140.0, 135.7, 130.3, 128.7, 126.2, 126.1 (Ar C), 45.9
(C-2), 38.0 (C-4), 28.1 (C-3), 21.3 (2 × Me), 19.1 (Me); MS m/z (%)
190 (M+, 5), 172 (1), 157 (1), 145 (1), 129 (2), 119 (53), 118 (52),
105 (100); HRMS: calcd for C13H18O[M + H+] 191.1430; found:
191.1428.
N-(tert-butyl)-1-(1-vinyl-1H-imidazol-2-yl)propan-1-amine (17):
IR (film, ν, cm−1) 1644, 1484. 1H NMR (CDCl3, 300 MHz): δ 7.59 (dd,
J = 15.8 and 8.8 Hz, 1H, CH2=CH), 7.13 (d, J = 1.2 Hz, 1H, =CHN=),
6.95 (d, J = 0.9 Hz, 1H, =CHN), 5.15 (dd, J = 15.8 and 1.2 Hz,
1H, =CHAH), 4.82 (dd, J = 8.8 and 1.2 Hz, 1H, =CHBH), 3.96 (t,
J = 7.2 Hz, 1H, CH), 1.57–1.78 (m, 2H, CH2), 0.97 (s, 9H, 3 × Me),
0.85 (t, J = 7.5 Hz, 3H, Me); 13C NMR (CDCl3, 75 MHz): δ 151.1,
129.8, 128.0, 115.4, 101.0, 52.9, 50.9 (tert-C), 30.8, 29.5 (3 × Me),
10.8; MS m/z (%) 207 (M+, 0.5), 192 (6), 178 (93), 150(1), 135 (88),
122 (100), 107 (5), 95 (15); HRMS: calcd for C12H21N3[M + H+]
208.1808; found: 208.1805.
2-Methy-4-phenylbutanal (4): The same procedure was applied as
described for 3 except the quench stage was performed with sat.
NH4Cl solution (50 mL). Oxalic acid (ca 5–8 g) was added portion-
wise until the aqueous phase had reached pH 3–4. The resulting
mixture was stirred at RT for 3 h. Work-up as described above and
further purification by column chromatography afforded 4,29–32 b.p.
95–97 °C/1.5−1 mbar. 1H NMR (CDCl3, 300 MHz): δ 9.62 (J 1.8 Hz,
1H, H-1), 7.15–7.30 (m, 5H, Ph), 2.58–2.72 (m, 2H, H-4), 2.30–2.44
(m, 1H, H-2), 1.99–2.13 (m, 1H, H-3A), 1.60–1.74 (m, 1H, H-3B), 1.15
(d, J = 7.0 Hz, 3H, 2-Me). 13C NMR (CDCl3, 75 MHz): δ 204.8 (C-1),
141.4, 128.5, 128.4(9) and 126.1 (Ar C), 45.6 (C-2), 33.1 (C-4), 32.2
(C-3), 13.4 (2-Me). MS m/z (%) 162 (M+, 5), 144 (2), 128 (2), 104
(100), 91 (48). The analytical and spectroscopic data of the other
products obtained by the same procedure are given below.
Syn- and anti-N-(tert-butyl)-1,2,5,6-tetrahydro-[1,1-biphenyl]-2-
1
amine (21 and 22) as a mixture: H NMR (CDCl3, 400 MHz): 21
δ 7.15–7.22 (m, 5H, Ph), 5.86–5.92 (m, 1H, H-3), 5.58–5.63 (m, 1H,
H-4), 3.04 (t, J = 4.8 Hz, 1H, H-2), 2.71–2.75 (m, 1H, H-1), 1.95–1.99
(m, 2H, CH2), 1.85–1.90 (m, 2H, CH2), 0.68 (s, 9H, 3 × Me); 13C NMR
(CDCl3, 100 MHz): δ 145.3, 128.5, 128.2, 128.0 (Ar C), 133.3 (C-3),
126.0 (C-4), 50.2 (tert-C), 48.1 (C-2), 46.5 (C-1), 30.3 (3 × Me),
24.9 (C-6), 23.3 (C-5); 22 δ 7.13–7.23 (m, 5H, Ph), 5.79 (app. dq,
J = 10.0 and 2.1 Hz, 1H, H-3), 5.62–5.68 (m, 1H, H-4), 3.20 (dt,
J = 7.8 and 2.1 Hz, 1H, H-2), 2.53 (ddd, J = 10.2, 7.8 and 3.4 Hz, 1H,
H-1), 1.82–1.94 (m, 4H, H-5, 6), 0.81 (s, 9H, 3 × Me); 13C NMR
(CDCl3, 100 MHz): δ 145.7, 128.2, 127.9, 127.6 (Ar C), 134.1 (C-3),
126.5 (C-4), 53.8 (C-2), 50.6 (tert-C), 49.3 (C-1), 29.7 (3 × Me), 28.9
(C-6), 24.9 (C-5); MS m/z (%) 229 (M+, 1), 214 (1), 171 (1), 157 (2),
141 (1), 125 (100), 110 (11), 91 (17); HRMS: calcd for C16H23N[M +
H+] 230.1903; found: 230.1903.
2-Phenethyl-4-phenylbutanal (12): Oil, IR (film, ν, cm−1) 1720
1
(C=O), 1602, 1495, 1454. H NMR (CDCl3, 300 MHz): δ 9.60 (d,
J = 2.5 Hz, 1H, CHO), 7.13–7.30 (m, 10H, Ph), 2.53–2.69 (m, 4H,
2 × CH2), 2.32–2.37 (m, 1H, CH), 1.95–2.07 (m, 2H, CH2), 1.72–1.84
(m, 2H, CH2). 13C NMR (CDCl3, 75 MHz): δ 204.5 (C-1), 141.3,
128.5, 128.4 and 126.1 (Ar C), 50.6 (C-2), 33.2 (CH2), 30.5 (CH2);
MS m/z (%) 252 (M+, 1), 234 (4), 148 (22), 130 (15), 104 (55), 92
(100), 90 (75), 77 (7); HRMS: calcd for C18H20O[M + H+] 253.1587;
found: 253.1586.
N-(tert-butyl)-3,5-dimethyl-1,2,5,6-tetrahydro-[1,1-biphenyl]-2-
1
amine (23): Oil, H NMR (CDCl3, 300 MHz): δ 7.19–7.26 (m, 5H,
Ph), 5.29 (brs, 1H, H-4), 2.96–3.06 (m, 1H, H-2), 2.78 (app. dt,
J = 12.1 and 3.1 Hz, 1H, H-1), 2.17–2.25 (m, 1H, H-5), 1.88 (s, 3H,
3-Me), 1.60–1.75 (m, 2H, H-6), 1.04 (d, J = 7.0 Hz, 3H, 5-Me), 0.57
(s, 9H, 3 × Me); 13C NMR (CDCl3, 75 MHz): δ 145.5, 129.4, 127.5
and 125.8 (Ar C), 137.4 (C-3), 130.4 (C-4), 55.0 (C-2), 49.9 (tert-C),
46.9 (C-1), 32.5 (C-5), 31.3 (C-6), 30.2 (3 × Me), 23.3 (Me), 21.9
(Me); MS m/z (%) 257 (M+, 1), 215 (2), 169 (3), 153 (100), 138 (16),
97 (48), 82 (14); HRMS: calcd for C18H27N[M + H+]258.2216; found:
258.2216.
2-Isopropyl-4-phenylbutanal (13),33 oil, 1H NMR (CDCl3, 300 MHz):
δ 9.67 (d, J = 3.0 Hz, 1H, CHO), 7.15–7.30 (m, 5H, Ph), 2.61–2.72
(m, 1H, HA-3), 2.43–2.58 (m, 1H, HB-3), 2.09–2.19 (m, 1H, H-2),
1.91–2.09 (m, 2H, H-4), 1.68–1.81 (m, 1H, CH), 0.96 (d, J = 6.7 Hz,
3H, CH3), 0.95 (d, J = 6.7 Hz, 3H, CH3); 13C NMR (CDCl3, 75 MHz):
δ 205.5 (CHO), 141.7, 128.4(3), 128.3(8) and 126.0 (Ar C), 57.6
Scheme 4 Double bond migration in the reaction of 20 and styrene.

JOURNAL OF CHEMICAL RESEARCH 2012 735
7
8
9
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4-Phenethylcyclohex-1-enecarbaldehyde (24): Oil, IR (film, ν,
1
cm−1) 1680 (C=O), 1642, 1495, 1453. H NMR (CDCl3, 300 MHz):
δ 9.42 (s, 1H, CHO), 7.16–7.31 (m, 5H, Ph), 6.78 (m, 1H, H-2), 2,71
(t, J = 7.8 Hz, 2H, PhCH2), 2.35–2.58 (m, 2H, CH2), 1.83–2.15 (m,
3H, CH and CH2), 1.58–1.71 (m, 3H, CH2 and H-5A), 1.19–1.37 (m,
1H, H-5B). 13C NMR (CDCl3, 75 MHz): δ 194.1(CHO), 150.7(C-2),
142.3, 141.6, 128.4, 128.3, 125.8, 37.9, 33.2, 33.0, 32.9 (C-4), 27.5,
21.1; MS m/z (%) 214 (M+, 34), 196 (4), 181 (3), 167 (2), 143 (11),
122 (13), 109 (37), 91 (100); HRMS: calcd for C15H18O[M +
H+]215.1430; found: 215.1430.
2-Phenethylcyclohex-3-enecarbaldehyde (25) and 1-Phenethylcy-
clohex-3-enecarbaldehyde (26): Oil, IR (film, ν, cm−1) were obtained
as a mixture from silica gel chromatography. 1H NMR (CDCl3,
300 MHz): δ 9.62 and 9.50 (two s, 1H, CHO), 7.08–7.35 (m, 5H, Ph),
5.73 and 5.69 (two brs, 2H, olefinic), 2.24–2.85 (m, 4H, PhCH2CH2),
1.53–2.18 (m, 6H, ring CH2 and CH); 13C NMR (CDCl3, 75 MHz):
δ 205.6 and 204.5 (CHO), 142.0 and 141.9 (Ar C), 129.0, 128.5,
128.4, 128.3, 128.2, 127.1, 126.9, 126.0, 125.9 and 124.4 (Ar C and
CH=CH), 51.0 (C-1 of 25), 48.2 (C-1 of 26), 37.7 and 36.5 (CH2),
33.8 (C-2 of 25), 33.0, (C-2 of 26), 30.2, 29.8, 27.4, 23.3, 22.3 and
21.0 (CH2); MS m/z (%) 214 (M+, 11), 196 (19), 185 (9), 168 (3), 143
(3), 129 (5), 117 (10), 105 (42), 91 (100); HRMS: calcd for C15H18O
[M + H+] 215.1430; found: 215.1430.
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